Frequency reuse method in an orthogonal frequency division multiplex mobile communication system

Abstract

A frequency reuse method in an OFDM mobile communication system is provided. Frequency resources available to each BS are divided into at least four frequency groups and a different or the same frequency reuse distance is set for each of the frequency groups. The frequency groups are sequentially assigned to cell areas of each BS such that lower frequency groups are available to a near cell area and higher frequency resource groups are available to a remote cell area.

What is claimed is:  
     
         1 . A frequency reuse method in an orthogonal frequency division multiplex (OFDM) mobile communication system having a plurality of base stations (BS), comprising the steps of: 
 dividing frequency resources available to each BS into at least four frequency groups and setting a frequency distance for each of the frequency groups; and    sequentially assigning the frequency groups to cell areas of each BS such that lower frequency groups are available to a near cell area and higher frequency resource groups are available to a remote cell area.    
     
     
         2 . The method of  claim 1 , wherein each of the frequency groups includes successive carriers.  
     
     
         3 . The method of  claim 1 , wherein when frequency hopping is adopted, the frequency resources are divided into the at least four frequency groups according to frequency hopping patterns.  
     
     
         4 . The method of  claim 1 , wherein at least one of the frequency groups is used with a frequency reuse distance of 1 in the near cell area.  
     
     
         5 . The method of  claim 4 , wherein the near cell area is defined according to a distance from the BS.  
     
     
         6 . The method of  claim 4 , wherein the near cell area is defined according to a system-required carrier-to-interference ratio (C/I).  
     
     
         7 . The method of  claim 7 , wherein the near cell area is defined according to interference from an adjacent BS.  
     
     
         8 . The method of  claim 1 , wherein the at least four frequency groups are of the same size.  
     
     
         9 . The method of  claim 1 , wherein a frequency group assigned to the near cell area satisfies  
       
         
           
             
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       where n 1  and n 2  are the numbers of frequency resources available to the near cell area and the remote cell area, respectively, λ 1  and λ 2  are the probabilities of generating an event in the near area and the remote area, respectively, and j is a parameter for summation.  
     
     
         10 . The method of  claim 9 , wherein the other frequency groups are of the same size and assigned to the remote cell area.  
     
     
         11 . A frequency reuse method in an orthogonal frequency division multiplex (OFDM) mobile communication system having a plurality of base stations (BS), comprising the steps of: 
 dividing frequency resources into at least four frequency groups;    assigning a predetermined one of the frequency groups to a near cell area of each BS; and    assigning the other three frequency groups with a frequency reuse distance of 3 to a remote cell area of each BS.    
     
     
         12 . A method of assigning frequency resources to mobile stations (MSs) in a base station (BS) having first frequency resources for a near cell area and second frequency resources for a remote cell area in an orthogonal frequency division multiplex (OFDM) mobile communication system, the method comprising the steps of: 
 determining a predetermined condition between the BS and an MS upon request of the MS for OFDM frequency setup;    establishing a channel with the MS by assigning a first OFDM frequency resource to the MS if the predetermined condition is satisfied; and    establishing a channel with the MS by assigning a second OFDM frequency resource to the MS if the MS is outside of the near cell area.    
     
     
         13 . The method of  claim 12 , wherein the predetermined condition is the distance between the BS and the MS.  
     
     
         14 . The method of  claim 12 , wherein the predetermined condition is the level of interference experienced by the MS from an adjacent BS  
     
     
         15 . The method of  claim 12 , wherein the predetermined condition is the strength of a received signal between the MS and the BS.  
     
     
         16 . The method of  claim 12 , wherein the first frequency resources are used with a frequency reuse distance of 1 in the near cell area.  
     
     
         17 . A method of assigning orthogonal frequency division multiplex (OFDM) frequency resources to mobile stations (MSs) in a base station (BS) in an OFDM system having a plurality of BSs, each BS communicating with MSs in OFDM, having at least two sub-channel groups, and assigning OFDM frequency resources to an MS requesting a communication, the method comprising the steps of: 
 comparing the signal to interference ratio (SIR) of an MS with a predetermined reference SIR, upon request for an OFDM frequency setup from the MS; and    assigning OFDM frequency resources in a low sub-channel group to the MS if the SIR of the MS is lower than the reference SIR.    
     
     
         18 . The method of  claim 17 , wherein if at least three sub-channel groups are set and at least two predetermined reference SIRs are used to discriminate the sub-channel groups, OFDM frequency resources in a sub-channel group corresponding to the lowest of reference SIRs higher than the SIR of the MS are assigned to the MS.  
     
     
         19 . The method of  claim 17 , wherein the sub-channel group for the MS is determined according to the SIR and lognormal fading-including signal loss of the MS.  
     
     
         20 . The method of  claim 19 , wherein a low-load sub-channel group is assigned to the MS if the MS has a great lognormal fading value.  
     
     
         21 . The method of  claim 17 , wherein the BS hops OFDM frequencies in the sub-channel group for the MS according to a frequency hopping rule preset during communication with the MS.  
     
     
         22 . A method of assigning orthogonal frequency division multiplex (OFDM) frequency resources to mobile stations (MSs) in a base station (BS) in an OFDM system having a plurality of BSs, each BS communicating with MSs in OFDM, having at least two sub-channel groups, and assigning OFDM frequency resources to an MS requesting a communication, the method comprising the steps of: 
 assigning, upon request for an OFDM frequency setup from the MS, to an MS OFDM frequency resources in a sub-channel group that maximizes load p in Eq. (10) and Eq. 911), when a channel is modeled as Eq. (8) and the average signal to interference ratio (SIR) of an MS spaced from the BS by a distance r is calculated by Eq. (9),                    Γ        (   d   )       =     c       d                α               (   8   )                 1   /     r                α           2        p        [         (     1       3     -   r       )     α     +       (     1     3   +     r   2     -       3        r         )     α     +       (     1     3   +     r   2     +       3        r         )     α       ]                 (   9   )               1         2        p        (     1   -     r   2       )          N       N   -     N   1              [         (     1       3     -   r       )     α     +       (     1     4   -     3         )     α     +       (     1     4   +     3         )     α       ]               (   10   )                 1   /     r                α               2      p                   r   2        N       N   1                  [         (     1       3     -   1       )     α     +       (     1     3   +     r   2     -       3        r         )     α     +                   (   11   )                              (     1     3   +     r   2     +       3        r         )     α     ]                                        where d is the distance between the BS and the MS, c is a constant determined by a frequency and an environment, α is a path loss exponent, a cell load is p, N is the number of entire sub-channels, and N 1  is the number of sub-channels assigned to an inner cell.